Rosie,
Lube oil isn't for greasing - it's for preventing your engines from seizing! (ha! Poetry!)
The oil has nearly the same viscosity as the oil in your car engine, and does exactly the same job - it lubricates the moving internal parts and prevents metal-to-metal contact (which would generate a hot spot, and probably lead to engine failure).
The oil also takes heat away from the internal components and transfers it to the engine cooling water, sometimes in a sea water cooler, and sometimes in a fresh-water cooled cooler (depends on manufacturers preferences).
And it's third purpose is to remove wear particles from inside the engine and carry them to the oil filters.
If you take a bucket half full of water and start swinging it backward & forward, eventually you will get water right up one side of the bucket, and have the bottom of the bucket nearly exposed on the other side. The water will 'surge' across the bucket as it is moved. Imagine the low oil level float being located on the side where the bottom of the bucket is nearly exposed - it will trigger a Low Level alarm.
However, the alarm response time is normally adjustable - ie., imagine if the oil tank level alarm delay is set for 15 seconds, and the alarm float switch is down for 10 seconds (indicating a low oil level), the alarm will not physically activate.
But, if the alarm delay is set for 5 seconds, and the float switch is down for 10 seconds the alarm will activate. This alarm does not shut the engine down - it just tells the duty engineer he needs to transfer some fresh oil from the storage tank to the engine sump tank. The alarm delay settings are there to enable the alarm activation time to be 'delayed' so as to prevent continuous false alarms when the fluids are surging around the tank in bad weather.
However, in the Viking Sky, the engines actually shut down. This means the engine oil levels in the sump tanks got so low that the oil pumps sucked air, the engine oil pressure dropped suddenly, and the engine oil pressure shutdown switch was instantly activated (no delay time allowed on this one!), and worked properly to protect the engine.
So, why didn't their engine's oil sump tank low level alarms activate early enough to give the engineers time to top up the oil levels before the shutdowns occurred? That is the big question!
When all this electronic control wizardry began being installed in ships back in the 70s & 80s, there used to be what was called a 'Function Test' button. Once a day we would press it, just before putting the engine room to bed. The Function Switch would instantly test ALL the many hundreds of alarm channels and ensure their integrity & functionality, and those circuits that had delays incorporated would indicate this by taking anything up to 30 seconds before their indicator light would begin flashing. So, after 30 seconds, I could, at a glance, scan all the channels to ensure they were all working before the engine room was left un-manned for the night. Passenger vessels are forbidden to operate with the engine control room un-manned, but that is no excuse for not testing the alarm circuits & functions.
However, as time has gone by, and the electronic complexity has increased, I have been seeing this facility to 'Function Test' all the channels has slowly disappeared. But, having said that, if one gets a broken wire on a circuit, it should pop up as a fault and tell the engineer it has failed.
Viking Sky should have low oil level float alarms in the sump tanks. Why did they not go off well before the engine oil pumps lost suction? Or are they fitted at the wrong level? Or, had someone, with all 4 alarms continually sounding off together, thought there must have been a common alarm system fault and muted the alarms? Trying to physically dip the tanks in that weather is hopeless - you have to bring the oil levels up to the correct marks before you hit the rough weather (knowing what was outside, they should have checked the levels while they were still navigating the 'Inside Passage'). It's called 'Anticipation' and 'Forethought'!
This ship had probably never been in weather so wild before (which makes me laugh - seeing the video footage, it was not really that rough! Cargo vessels normally plod straight through that stuff every day, but cruise ships desperately try to avoid it because they want their passengers to return another day).
I will be awaiting the MAIB report with interest.
Cheers,
Skilly
ps - interesting to note Viking Sky's engines are smaller models of those fitted to QE2
Topic: Accidents and mishaps at sea (Read 126197 times)